Retractors serve to pull a tooth in a certain direction by exerting a tractive force, or to tilt a tooth by exerting a torque so as to correct dental misplacement. A first known retractor consists of a single wire member which--starting from one end--is first of all bent towards one side at an approximate right angle, then forms a spring with one turn (3.times.180.degree.) and subsequently extends with one wire portion beyond the longitudinal axis of the retractor to the upper side, where the wire forms two loops oriented in the direction of the reactor ends. The wire then extends beyond the longitudinal axis of the retractor again to form over the aforementioned spring a second identical spring, from which the wire extends back to the longitudinal axis of the retractor and after making a bend of approximately 90.degree. forms the continuation of this longitudinal axis. In order to obtain the necessary spring path, the wire portions of this known retractor that lead to the spring turns must be relatively long, and, in addition, wire turns are located beyond, i.e., on either side of the longitudinal axis of the retractor. For this reason, this known retractor is extremely vulnerable to becoming distorted in shape, for example, by the tooth brush when the teeth are being cleaned. Furthermore, it is annoying to have parts of the retractor protruding on either side of the longitudinal axis of the retractor. Finally, the known retractor is rather unstable in the face of torsional stress, which has a negative effect on the accuracy of the dental misplacement correction.
A retractor of the kind mentioned at the beginning comprising a tube with two openings, which is displaceable on the first wire member, and in which the second wire member is also guided in a longitudinally displaceable manner is also known. In order to avail over the necessary spring path for activation of the retractor, the area of the first wire member carrying the pressure spring is of relatively long design, and since this area is bent approximately in the center, it tends to prick the gum when the retractor is being worn. Moreover, the tube with two openings is relatively large and causes an annoyance when worn. Finally, the first wire member engaging with the tooth which is to be corrected, is relatively rigid, whereas, in actual fact, as great a flexibility as possible is desired.
The object underlying the invention was to produce a retractor which despite an adequate path for the activation and desired flexibility of the wire member which engages with the tooth to be corrected, is smaller than the first above-described known retractor and cannot be as easily distorted in shape as the latter. In order to achieve this object a retractor of the kind mentioned at the beginning is designed in accordance with the invention such that the second wire member is attached to the tube having one opening, and in that the first wire member forms a spring comprising two legs and two turns (approximately 5.times.180.degree.) located between said legs, the ends of said turns extending around approximately right-angled bends to issue in the wire member ends. Two things are achieved by combining such a spring with a helical spring: Firstly, the helical spring can be of shorter design, so that the area of the first wire member carrying the helical spring does not protrude as far from the longitudinal axis of the retractor, even when this area is bent. Furthermore, the desired flexibility of the first wire member is attained thereby. Nevertheless, the retractor according to the invention is more stable in the face of torsional stress than the known first above-described retractor. At the same time, the necessity of using a tube comprising two openings, as in the case of the second above-described known retractor, is eliminated.
The known retractors are made from a 0.41.times.0.41 mm four-edged steel wire. It has now become evident that the quality of the guidance of the two wire members along each other can be substantially improved if the first wire member consists of 0.41.times.0.41 mm four-edged wire, and the second wire member of 0.41.times.0.46 mm four-edged wire. Furthermore, in the case of the retractor according to the invention, the guidance play occurs only in one single tube, and not, as in the case of the known retractor of the kind mentioned at the beginning, in two tubes.
In a preferred embodiment of the retractor according to the invention, the springs are so designed that a tractive force of approximately 100 to 120 grams corresponds to an activation of the retractor by 2 mm, and a tractive force of approximately 140 grams corresponds to an activation of 3 mm.